Food Webs

Status and Trends
some major changes; trends for many unknown
Concern, some getting worse at slow to moderate rate; for others, rate of change unknown
data only for some parts of food webs and some regions
Medium confidence in finding
early indications of changes in some population cycles
Red flag

KEY FINDING 20. Fundamental changes in relationships among species have been observed in marine, freshwater, and terrestrial environments. The loss or reduction of important components of food webs has greatly altered some ecosystems.

This key finding is divided into three sections:

Food webs are formed through linkages of the different organisms in a system, building on the primary producers (plants, algae, and microorganisms), and involving an array of consumers and decomposers.1 Population cycles are regular periodic peaks and lows in animal abundance that are driven largely by the dynamics of some food webs. Food webs and population cycles are important because they shape the structure and function of ecosystems. Changes in species diversity are often related to changes in food webs.

An example of the far-reaching effects of severe reductions in an important part of a food web is the decline of cod and other predatory fish off the Atlantic coast. This loss of fish predators led to further ecosystem shifts, with, for example, large increases in shrimp (see Marine Biome).

 

 

Key finding overview